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compiler/Diagnostic.cs

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+namespace Compiler;
+
+public sealed class Diagnostic(DiagnosticSeverity severity, string message, string? help, FileInfo? file)
+{
+    public static DiagnosticBuilder Info(string message) => new DiagnosticBuilder(DiagnosticSeverity.Info, message);
+    public static DiagnosticBuilder Warning(string message) => new DiagnosticBuilder(DiagnosticSeverity.Warning, message);
+    public static DiagnosticBuilder Error(string message) => new DiagnosticBuilder(DiagnosticSeverity.Error, message);
+
+    public readonly DiagnosticSeverity Severity = severity;
+    public readonly string Message = message;
+    public readonly string? Help = help;
+    public readonly FileInfo? File = file;
+}
+
+public sealed class DiagnosticBuilder(DiagnosticSeverity severity, string message)
+{
+    private FileInfo? file;
+    private string? help;
+
+    public DiagnosticBuilder At(string fileName, int line, int column, int length)
+    {
+        file = new FileInfo(fileName, line, column, length);
+        return this;
+    }
+
+    public DiagnosticBuilder At(string fileName, Token? token)
+    {
+        if (token != null)
+        {
+            At(fileName, token.Line, token.Column, token.Length);
+        }
+
+        return this;
+    }
+
+    public DiagnosticBuilder At(string fileName, Node? node)
+    {
+        if (node != null && node.Tokens.Count != 0)
+        {
+            // todo(nub31): Calculate length based on last token
+            At(fileName, node.Tokens[0]);
+        }
+
+        return this;
+    }
+
+    public DiagnosticBuilder At(string fileName, TypedNode? node)
+    {
+        if (node != null && node.Tokens.Count != 0)
+        {
+            // todo(nub31): Calculate length based on last token
+            At(fileName, node.Tokens[0]);
+        }
+
+        return this;
+    }
+
+    public DiagnosticBuilder WithHelp(string helpMessage)
+    {
+        help = helpMessage;
+        return this;
+    }
+
+    public Diagnostic Build()
+    {
+        return new Diagnostic(severity, message, help, file);
+    }
+}
+
+public sealed class FileInfo(string file, int line, int column, int length)
+{
+    public readonly string File = file;
+    public readonly int Line = line;
+    public readonly int Column = column;
+    public readonly int Length = length;
+}
+
+public enum DiagnosticSeverity
+{
+    Info,
+    Warning,
+    Error,
+}
+
+public sealed class CompileException(Diagnostic diagnostic) : Exception
+{
+    public readonly Diagnostic Diagnostic = diagnostic;
+}
+
+public static class DiagnosticFormatter
+{
+    public static void Print(Diagnostic diagnostic, TextWriter writer)
+    {
+        var (label, color) = diagnostic.Severity switch
+        {
+            DiagnosticSeverity.Info => ("info", Ansi.Cyan),
+            DiagnosticSeverity.Warning => ("warning", Ansi.Yellow),
+            DiagnosticSeverity.Error => ("error", Ansi.Red),
+            _ => ("unknown", Ansi.Reset),
+        };
+
+        writer.Write(color);
+        writer.Write(label);
+        writer.Write(Ansi.Reset);
+        writer.Write(": ");
+        writer.WriteLine(diagnostic.Message);
+
+        if (diagnostic.File is null)
+            return;
+
+        var file = diagnostic.File;
+        var lineNumberWidth = diagnostic.File.Line.ToString().Length;
+
+        writer.WriteLine($" {new string(' ', lineNumberWidth)}{file.File}:{file.Line}:{file.Column}");
+        writer.WriteLine($"{new string(' ', lineNumberWidth)} | ");
+
+        var sourceLine = TryReadLine(file.File, file.Line);
+        if (sourceLine != null)
+        {
+            writer.Write($"{file.Line.ToString().PadLeft(lineNumberWidth)} | ");
+            writer.WriteLine(sourceLine);
+
+            writer.Write(new string(' ', lineNumberWidth));
+            writer.Write(" | ");
+            writer.Write(new string(' ', file.Column - 1));
+            writer.Write(color);
+            writer.Write(new string('^', Math.Max(1, file.Length)));
+            writer.WriteLine(Ansi.Reset);
+        }
+
+        writer.WriteLine($"{new string(' ', lineNumberWidth)} |");
+
+        if (!string.IsNullOrWhiteSpace(diagnostic.Help))
+        {
+            writer.WriteLine($"   = help: {diagnostic.Help}");
+        }
+    }
+
+    private static string? TryReadLine(string file, int line)
+    {
+        try
+        {
+            using var reader = new StreamReader(file);
+            for (var i = 1; i < line; i++)
+            {
+                if (reader.ReadLine() == null)
+                    return null;
+            }
+
+            return reader.ReadLine();
+        }
+        catch
+        {
+            return null;
+        }
+    }
+
+    private static class Ansi
+    {
+        public const string Reset = "\e[0m";
+        public const string Red = "\e[31m";
+        public const string Yellow = "\e[33m";
+        public const string Cyan = "\e[36m";
+    }
+}